Alexander disease is a rare, fatal degenerative disease, classified among the leukodystrophies because of the severe hypomyelination seen in young infants or the demyelination seen in older children. The pathological signature of the disorder is the Rosenthal fiber, an accumulation of intermediate filaments and small heat shock proteins in astrocytes throughout the CNS. Sequencing the GFAP gene revealed single base changes in the coding region, predicting, non-conservative amino acid substitutions, in 12 of 13 patients examined to date. All mutations are heterozygous, suggesting a dominant, gain-of-function mechanism. Alexander disease therefore represents the first example of a primary genetic disorder of astrocytes, one of the major cell types in the vertebrate central nervous system. The goals of this Program Project are to investigate the means by which GFAP mutations lead to inclusion bodies, disruption of the astrocyte cytoskeleton, astrocyte, dysfunction, and severe consequences for oligodendrocytes in the central nervous system. We will continue genetic studies of Alexander disease patients with unusual clinical presentations to clarify the range of disorders associated with GFAP mutations; develop animal models carrying the same mutations as those identified in humans; and explore potential approaches for interfering with the effects of the mutant protein. Our studies span molecular, biochemical, cellular, and morphological approaches to these questions. The Program will link four laboratories; three of these already have a proven record of productive interactions, and a fourth group will bring unique expertise in studying filament assembly. The Program will promote an expanded effort on the role of glial filament dysfunction in disease, by fostering sharing of reagents, animals, and results between the four labs, cross-fertilization of ideas, and regular communication and meetings among laboratory members. These studies promise novel insights into the role of glial filaments in the cell biology of astrocytes, and the role of astrocytes in brain function and disease.